On the Functional Group Tolerance of Ester Hydrogenation and Polyester Depolymerisation Catalysed by Ruthenium Complexes of Tridentate Aminophosphine Ligands

Abstract

Abstract:The synthesis of a range of phosphine-diamine, phosphine-amino-alcohol, and phosphineamino-amide ligands and their ruthenium(II) complexes are reported. Five of these were characterised by X-ray crystallography. The activity of this collection of catalysts was initially compared for the hydrogenation of two model ester hydrogenations. Turnover frequencies up to 2400 h -1 were observed at 85 o C. The catalysts turnover, albeit slowly at near ambient temperatures. Using a phosphine diamine Ru(II) complex that was identified as the most active catalyst, a range of aromatic esters were reduced in high yield. The hydrogenation of alkene-, diene-, and alkyne functionalised esters was also studied. Substrates with a remote, but reactive terminal alkene substitutent could be reduced chemoselectively in the presence of 4-dimethylaminopyridine (DMAP) co-catalyst. The chemoselective reduction of the ester function in conjugated dienoate ethyl sorbate could deliver (2E,4E)-hexa-2,4-dien-1-ol, a precursor to leaf alcohol. The mono-unsaturated alcohol (E)-hex-4-en-1-ol was produced with reasonable selectivity, but complete chemoselectivity of C=O over the diene is elusive. High chemoselectivity for the reduction of an ester over an alkyne group was observed in the hydrogenation of an alkynoate for the first time. The catalysts were also active in the depolymerisation reduction of samples of waste PET to produce benzene dimethanol. These depolymerisations were found to be poisoned by the ethylene glycol side product, although good yields could still be achieved.

Molecular catalyst systems as key enablers for tailored polyesters and polycarbonate recycling concepts

“…More recently, the group of M. Clarke enhanced the hydrogenolysis of PET by using innovative ruthenium-N,N,P-pincer complexes. However, high catalyst loadings, complex solvents, and long reaction times hamper so far the translation of this approach to consumer products and engineered polymers ( 19 ).…”

Polyethylene Terephthalate Deconstruction Catalyzed by a Carbon‐Supported Single‐Site Molybdenum‐Dioxo Complex

“…[19] Furthermore, C/MoO 2 can be easily recovered by filtration and reused with negligible Mo leaching or activity loss. [15,18] These characteristics raise the intriguing question of whether C/MoO 2 might provide a platform for transesterification and hydrogenation processes useful in polyester recycling. Here we report an efficient solventless PET depolymerization process catalyzed by C/ MoO 2 , yielding the starting monomer, terephthalic acid (PTA), and ethylene as the major products (Figure 1 C).…”

Synthesis and characterization of polyethylene terephthalate (PET) precursors and potential degradation products: Toxicity study and application in discovery of novel PETases

“…The resulting pyridinium salt was J o u r n a l P r e -p r o o f filtered, and filtrate was washed successively with saturated aqueous CuSO 4 , water, saturated NaHCO 3 and brine, then dried over Na 2 SO 4. The organic solution was concentrated and residue was purified by dry flash chromatography (SiO 2 ; eluent: dichloromethane/petroleum ether/ethyl acetate = 60:40:5), to afford of diester 8 as a white solid (10.25 g, 63%, mp 163 o C) (Fuentes et al, 2015). 1 H NMR (400 MHz, CDCl 3 ): δ H 8.10 (brs, 8H), 4.70 (s, 4H), 3.94 (s, 6H).…”